Low-dose radiation from mammograms and chest X-rays may increase the risk of breast cancer in young women who are already at high risk because of family history or genetic susceptibility, Dutch researchers said on Tuesday.
They said high-risk women, especially those under 30, may want to consider switching to an alternative screening method such as magnetic resonance imaging, or MRI, which does not involve exposure to radiation.
"Our findings suggest that low-dose radiation increases breast cancer risk among these young, high-risk women, and a careful approach is warranted," said Marijke Jansen-van der Weide of the University Medical Center Groningen in the Netherlands.
"I should recommend to be careful with radiation before 30 and to think about alternatives," Jansen-van der Weide, who presented her findings at the Radiological Society of North America meeting in Chicago, said in a telephone interview.
For the study, Jansen-van der Weide pooled data from six published studies that involved 12,000 high-risk women from Europe and the United States.
The team found that of the 8,500 women who had been exposed to radiation from chest X-rays or mammograms before the age of 20 or those who had had five or more exposures were 2.5 times more likely to develop breast cancer than other high-risk women who had not been exposed.
The findings apply only to high-risk women, and not to women of average risk for breast cancer, but they may fuel confusion among women in the United States about the risks and benefits of mammography screening.
Last month, the U.S. Preventive Services Task Force, a federal advisory panel, recommended against routine breast mammograms for women in their 40s to spare them some of the worry and expense of extra tests to distinguish between cancer and harmless lumps.
Those recommendations contradicted years of messages about the need for routine breast cancer screening starting at age 40, sparking a rebellion from breast cancer specialists who argued the guidelines would confuse women and result in more deaths form breast cancer.
Robert Smith, director of cancer screening from the American Cancer Society, said the study by Jansen-van der Weide is an important area of investigation. "We know that breast tissue is susceptible to the harmful effects of radiation when women are at a young age, and that this risk diminishes as women age," Smith said in an e-mail.
But he said no individual study has shown that mammography increases the risk of breast cancer in women at average or high risk of breast cancer, and estimating how much mammography might increase the risk can vary widely.
"For now, the unavoidable conclusion is that the benefits of early breast cancer detection in women at very high risk outweigh the low possibility of a radiation-induced breast cancer," he said.
Jansen-van der Weide said the findings are based on a small sample, but when data from the studies were pooled they did reach statistical significance.
She said more studies are needed to get a more accurate estimate of the effect, but added, "I think these results also say there is something happening."
The American Cancer Society and other groups recommend that women at very high risk of breast cancer -- because of being positive for a genetic mutation in a breast cancer susceptibility gene or because of family history -- should get both an MRI and mammogram starting at age 30.
Although MRIs alone are more sensitive than mammograms, they are also more likely to turn up false-positive results.
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